Chapter 6. What does quantum theory mean?

[Technical note: The fundamental equation that must be solved in quantum
physics is the Schrödinger equation:

iħ ∂y∕∂t=Hy

This equation is explicitly a first-order differential equation in time, but
is implicitly second order in space since H is second order in the
spatial derivatives. The equation describes how the Schrödinger wavefunction
y propagates in time and space. It must be solved explicitly for
y.]

In contrast with classical physics, in which the results of an observation
are implicit in the theory itself, quantum theory requires an interpretation to
relate the wavefunction y to an observation.
There are three broad categories of interpretations.

6.1.1. Purely objective interpretations

In a "hidden variables" interpretation, Schrödinger's equation
is correct but incomplete as it stands. In this interpretation, quantum
theory must be supplemented by the addition of classical particles, which
are always present. These particles are assumed to have definite positions
and velocities but they are unknown so are called hidden variables. The wavefunction is not interpreted as a probability
function, but as the
source of a quantum force (also a hidden variable) which acts on the particles in addition to
the classical forces of electromagnetism and gravity.
In its pure objectivity, this interpretation is the most like classical
physics.

6.1.2. Partly objective and partly subjective interpretations

a) In the Copenhagen interpretation, the wavefunction
exists objectively prior to an observation. At the moment of observation,
the wavefunction collapses to describe the results of the observation. In
this interpretation, quantum theory is either incorrect or incomplete as it stands because
it must be modified to
describe the
phenomenon of wavefunction collapse. Because collapse is not
understood, this is sometimes called the "shut up and calculate" school, a
term attributed to American physicist David Mermin,
Physics Today, May 2004, p. 10. If conscious observation is assumed
to be what
collapses the wavefunction, this interpretation is partly subjective. If
some as yet uncertain, nonstandard, objective mechanism collapses the
wavefunction, this interpretation is purely objective.

b) In the "many-worlds" interpretation, the wavefunction is
assumed to be primary and unchanged by observation. However, at the moment
of observation, each possibility in the wavefunction manifests in an
observed world so there are as many observed worlds as there are
possibilities. Because branching requires observation, this interpretation
is partly subjective.

c) In the interpretation of Christopher Fuchs, there is an objective
system but there is no wavefunction. However, everything we know about the system is
in the form of subjective beliefs.

6.1.3. Purely subjective interpretations

Some physicists think that, if there is an objective
reality, it is not described by quantum theory. They think the theory can be
used only to calculate the probabilities for the different possible outcomes
of a given observation. To them, this is the only
interpretation that quantum theory has. This can be called a subjective
interpretation because the wavefunction reflects only our knowledge of a
situation rather than describing an objective reality.

One reason we abandoned classical particles was because we showed they could
not go through two slits at once and produce interference, whereas waves could
(see Section 4.1).
But interference is possible with classical particles if there is also a wave
present. A theory that includes both is the hidden variable theory developed by
David Bohm (1917 - 1992) [brilliant, unconventional American-Brazilian physicist who left the U.S. never
to return after
being blacklisted in 1949 by Senator Joe McCarthy during the anticommunist
hysteria,
was arrested and charged with contempt of Congress after pleading the Fifth
Amendment and refusing to recant his Marxism, was fired by Princeton University,
was later acquitted by the court but lost his American citizenship]. This is the best developed and best
known of the
hidden variable models. This model is fully deterministic and assumes that the
particles are classical and are subject to classical forces (which are all
local). However,
they are also
subject to a quantum force that is derived from a wavefunction. [To be more
accurate, there is a quantum potential that is derived from the wavefunction, and the quantum force is derived from the quantum potential.] The wavefunction is now not a probability wave.
Since the particles are assumed to be classical, their positions and velocities
are always definite, even before an observation. Contrary to the Copenhagen
interpretation, the wavefunction in the hidden-variables interpretation is not a
complete description of the system because the particle positions are also
required. In the initial state, the wavefunction specifies the actual
distribution of particles in space, not just a probability. The time development
of the wavefunction is then described by Schrödinger’s equation, as in
ordinary quantum theory.

Although the wavefunction now has a different interpretation, it is
mathematically identical with that in the Copenhagen quantum interpretation and
contains all parts of the waves, e.g., reflected and transmitted parts, or the
parts going through different slits, even if none of the particles follow those
paths. (A peculiarity of the quantum force is that it can be very large even
where the wavefunction is very small.) Since the wavefunction, and therefore the
quantum force, depends on all parts of the experimental apparatus (e.g., in a
two-slit experiment), so do the
particle trajectories, even though trajectories and apparatus may be quite
distant from each other. The result is that the quantum force from all
parts of the apparatus acts simultaneously on
all of the particles--hence, it is nonlocal.

Since the particles in a hidden-variables interpretation are assumed to be
classical,
there is no wavefunction collapse, and therefore it is not necessary to
introduce consciousness into the interpretation. Hence, hidden-variables
theories are consistent
with scientific materialism (see
Section 1.2). They are examples of "realist" theories
because they assume that the particles are real particles, not just quantum
waves.

Question: If the hidden variables interpretation were correct, how
would your life be affected?

The Bohm theory is not the only possible hidden-variables theory. However, we
have already seen that the
Aspect experiments excluded all local hidden-variables theories, while the Gröblacher
experiments excluded most hidden variables theories whether they are local
or not (Section
4.3). Because of these experiments, we shall conclude that it is not likely
that hidden-variables
theories describe reality.

In this interpretation, before an observation there are no particles, only a wavefunction that is a complete description of the system.
No other information about the system is possible. At the moment of observation,
the wavefunction must change from a probability wave
that includes all of the possibilities that existed before the observation to
one that describes only the possibility that is observed.
This is called reduction, or collapse, which is not explained by the theory. In
this interpretation, the wavefunction is the only external, objective reality that exists prior to an
observation.

The Copenhagen interpretation
is so named because it was formulated at Niels Bohr's Copenhagen institute in the 1920s. That
the wavefunction is the only objective reality is summed up in Bohr's statement, "There is
no quantum world. There is only an abstract quantum description" (quoted in Nick
Herbert's book, Quantum Reality (1985) p. 17), and in the statement of John Archibald
Wheeler (1911- 2008, brilliant American theoretical physicist and
cosmologist who coined the term "black holes"): "No elementary phenomenon is a real phenomenon
until it is an observed phenomenon" (quoted in Herbert's book, p. 18).

(In this and the following two sections, we draw heavily on
Chapter 11 of the 1990 book by Euan Squires, Conscious Mind in the
Physical World.) We will first show that any system that is completely described by quantum
theory cannot exhibit wavefunction reduction.

In order to do this in the most
efficient manner, we will use a symbolic notation that makes the description
concise and precise. Do not let this frighten you--it is simply a notation, not
higher mathematics. The notation will refer to a particular type of experiment
with particles that have spin. The spin of a particle is related to its
rotation. A macroscopic analog is a spinning top. We can say that if the top is
spinning normally on a flat, smooth surface, the spin (like the top) is pointing
down. If for some reason, the top flips so that it spins upside down (there are
tops that do this), we can say the spin is pointing up. Particles with spin
(like the electron) can have their spins pointing either up or down.

We start with an experiment in which an incoming electron is in a
superposition of spin-up (+) states and spin-down (-) states. By superposition,
we mean that the wavefunction is a sum of two terms, one describing the + state,
and one describing the - state. The superposition sums all of the possible
states of the system. This is an example of what is called a "pure" state. The
notation we now introduce is called the Dirac "ket" notation. Instead
of writing the wavefunction simply as y as we did
before, we enclose it in ket brackets and write çy>. We
use the same kind of notation for the + and the - states, and obtain

çy> = aç+> + bç->

All this equation says is that the electron is a wavefunction consisting of a
superposition of a spin-up component and a spin-down component. Here,
çaç2 is the
probability that an observation would see a spin-up particle, and çbç2 is the
probability that it would see a spin-down particle. (These are written
with absolute value signs because a and b
are in general complex quantities. However, this detail need not concern us
here.)

We now send this electron into a "Stern-Gerlach" apparatus. This
contains a nonuniform magnetic field which causes the ç+> component of the
wavefunction to go upward and the

ç-> component to go downward. Therefore, after the electron passes through
the apparatus, the Schrödinger equation tells us that it is described by the
pure state wavefunction,

çy> = aç+,up> + bç-,down>

where it is obvious that
ç+,up> goes up and ç-,down> goes down. This wavefunction is not arbitrary--given the
initial state wavefunction and the
characteristics of the Stern-Gerlach apparatus, the Schrödinger equation
dictates this form. We now send the electron into a detector, which
records "on" if the ç+> component is detected and
"off" if the ç-> component is detected. (The labels "on" and "off" are
purely arbitrary. They could also be called, e.g., "1" and
"0".) To make this clear, a diagram is shown below.

We assume that the detector, like the rest of the system, is described by the
Schrödinger equation. We must then include the state of the detector in the wavefunction, and the pure state becomes

çy> = aç+,up,on> + bç-,down,off>

This leads to a very important conclusion. Any object in the system that
can be described by the Schrödinger equation must be included in the
superposition of terms describing the system. The Schrödinger
equation always converts a pure state into a pure state. A pure state
wavefunction will always be a superposition, which means that there is a
probability of finding the system in either state.

Reduction, or collapse, of
the wavefunction requires going from a pure state consisting of a superposition
to a final state consisting of only one term because the reduced wavefunction
must describe the detector being in either one state or the other, but not both. Therefore, no object that can be described by the Schrödinger equation can
reduce the wavefunction, i.e., make an observation.

Now suppose that I look at the detector and that I also can be described by
the Schrödinger equation. Two components are needed to describe me, which we will
call me+ and me-, with the obvious connotations. The
final wavefunction will be the pure state,

çy> = aç+,up,on,me+> + bç-,down,off,me->
(final wavefunction)

However, if I am aware of the final state of the detector, this wavefunction
cannot describe the combined system since I know that the detector is either in
the "on" state or the "off" state. Something has effectively
collapsed the wavefunction so that only one term remains.

In the Schrödinger cat paradox of Section
4.2, I observe the cat in either the live state
or the dead state, not both. If consciousness collapses the wavefunction, it is either
my consciousness or the cat’s that does it. It is a metaphysical question
which of the two consciousnesses it is because what I see when I open the box will be
exactly the same in both cases.

Because most physicists are materialists and believe that consciousness is at
most an epiphenomenon, they do not like to admit that consciousness could
collapse the wavefunction since an epiphenomenon could not have the power of
agency. Rather, they prefer to think that some physical
mechanism such as the decoherence described in
Section 6.7 causes collapse. However, decoherence does not describe
collapse. It only explains the disappearance of interference between the two
terms of the wavefunction.

In the Copenhagen interpretation, wavefunction reduction defines the forward
direction of time because the reduced state is irreversible. This is
true for both microscopic and macroscopic systems. Recall
from
Section
2.3 that, in classical physics, the second law of thermodynamics
determined the forward direction of time because macroscopic
natural processes are statistically irreversible. In classical physics, irreversibility is a property of
a system whether or not it is observed, while in the Copenhagen interpretation,
irreversibility is a result of observation itself.

In this section, we shall assume the Copenhagen interpretation. We also
assume that the incoming wavefunction represents a single electron. We now suppose that we have a Stern-Gerlach experiment with two detectors
instead of one, as shown in the figure below. One detector is set up to record the ç+,up>
part of of the electron wavefunction, and
the other is set up to record the ç-,down> part. The detectors may be arbitrarily far apart. At the instant of
wavefunction collapse, what prevents
both detectors from simultaneously recording the electron? This example shows that
no local process can collapse the wavefunction because such processes
cannot prevent simultaneous or near-simultaneous coincidences between the detectors. Hence, we must conclude
that wavefunction collapse cannot be produced by any known physical process
(which are all local). (This result also can be inferred from the
Bell-Aspect experiments, see
Section 4.3.) Since the wavefunction collapses over all parts of space
simultaneously or nearly simultaneously, it is an intrinsically nonlocal phenomenon. Thus, any interpretation of quantum theory requiring wavefunction collapse is not consistent with a
local theory of reality, or with a philosophy such as materialism or scientism (see
Section 1.2).

Now suppose there are two observers, you and I (see figure below), so that you observe the ç-,down> state while I
simultaneously observe the ç+,up>
state. Then when I observe my detector to record "on", you must observe your
detector to record "off" because there is only one electron. Thus, if consciousness collapses the wavefunction,
it must be the same consciousness that collapses it at both detectors.
Therefore, there can be only one consciousness and it must be nonlocal.

This conclusion can be illustrated in a much simpler example than the
experiment described above. We still assume that an object is represented
by a wavefunction prior to an observation. Now suppose two observers
make simultaneous observations of the same object whose color is unknown before
the observation. In this case all possible colors must be represented in the wavefunction of the object before it is observed. Then why do both observers
observe the same color rather than one observer observing, for example, a red
object and the other observing a blue object? If consciousness collapses the wavefunction, the answer must be that the consciousness of both observers is the
same consciousness. Thus, the consciousness of all sentient observers
is the same nonlocal universal consciousness.

If the wavefunction is considered to be objectively real and the observation
is considered to be subjective, the Copenhagen interpretation is a modern example of Cartesian dualism (see
Section 1.3).

Problem: Suppose you live on the Starship Enterprise and I live on
earth 4 light-years away. By communicating with each other using
powerful laser signals, we have decided to make simultaneous
observations on the date Stardate 2200.0 to look for a lone hydrogen
molecule that we know from previous measurements (don’t ask) is coming
from type 1C supernova 2199K. We don’t know whether we will be able to
observe it but if we do, only one of us will be able to do so since the
wavefunction represents only one such hydrogen molecule.

The wavefunction of the hydrogen molecule extends over all space and
represents a molecule that could be anywhere in space. If the molecule
is observed, the Copenhagen interpretation says that the wavefunction
immediately collapses to one that is allowed by the observation. This
means that the wavefunction is now confined to a small region of space
near either you or me but not both.

During our observation, there is no time for any kind of signal to pass
from you to me or me to you. The wavefunction itself does not predict
which one of us will observe the molecule. It only predicts that there
is a certain probability that you will see it and a certain probability
that I will see it. So why can’t we both observe the molecule
simultaneously? (Don’t say it’s because there is only one molecule—there
is no molecule at all until it is observed. Until then, there is only a
wavefunction.)

Now let us consider the Stern-Gerlach experiment but without reference to quantum theory.
In this case, there is no wavefunction before observation. It
is apparent now that the consciousness of the observers must be universal
consciousness if both observers are to see the same object. Thus, whenever we
assume that objects appear only as mental images, not as independently existing
objects, the consciousness of the individual observers must be universal
consciousness. Of course, in this example, even the observers themselves
must be mental images.

In everyday life, we think that different observers see the same object
because the objects are objectively present. Thus, we are unaware that
universal consciousness is the only consciousness that is operating.

Question: Assume there is no objective reality. You see
a red object and I see a blue object.
What is a possible resolution
of this conflict?

This interpretation was invented by Hugh Everett (1930-1982) in 1957 as a theory
that would not require wavefunction collapse.

[Biographical note: Hugh Everett published his many-worlds theory as his Ph.D.
thesis at Princeton University under John Wheeler. In 1959, his theory was scorned
by Neils Bohr (who was wedded to the Copenhagen interpretation) but by this time
Everett had already left physics to join the Pentagon to work on mathematical weapons policy
research. He later co-founded several companies, which continued to do weapons studies for the military. He promoted the use of game theory in weapons policy, and helped
to create the policy
of Mutual Assured Destruction to prevent the U.S. from launching preemptive nuclear war
against the USSR and China, which he had calculated
would lead to unacceptable loss of life.]

Many-worlds theory was later adopted by cosmologists to describe the early
universe. According to cosmology, the universe exploded from a point at the time
of the big bang approximately 14 billion years ago. Early on, the universe was
so tiny and its density was so high that its gravitational forces were
enormously high. In such conditions, gravity cannot be treated classically so
it must be described quantum mechanically. Even though as yet there is no quantum theory of gravity,
physicists
think that the initial universe must be
described by a wavefunction. By definition, in this case, there can be no
external observer. Therefore, there can be no wavefunction collapse, and quantum theory is assumed to be correct without any
corrections or additions.

Let us now look at the Stern-Gerlach experiment in the light of the
many-worlds interpretation. We return to the wavefunction that describes my
observation of the detector:

çy> = aç+,up,on,me+> + bç-,down,off,me->
(Eq. 1)

There can be no reduction of the wavefunction now. Both terms must describe
reality. The many-worlds interpretation says that at the moment of an
observation, the world splits, or branches, and that both branches continue
after the observation. There is a me in both branches. This interpretation maintains that in each branch, the me in that branch is aware of
only the observation that it made. Since in myworld, I am aware of only
one result, I exist only in my branch. In the other branch, the other me is
aware of the other result. The two branches do not communicate with each other,
so the two mes are unaware of each other.

[Technical note: Assuming all of this to be true, what then is the
interpretation of a and b? The probabilistic interpretation of quantum theory says that çaç2 and çbç2
are the statistical probabilities of each outcome. These probabilities can be
measured only by making many observations on identical systems. What can they
mean here when we have only one system (the universe)? Bryce S. de Witt in 1970 proposed
the following interpretation. In the first trial of such an experiment, both
branches result
from the observation. If I now make many observations with my apparatus in my
branch, I will measure probabilities that agree with çaç2 and çbç2. At each
observation, there will be another branching, which will result in this me being
in my branch, and another me being in another branch. If each of these other mes
continues the observations, he will also measure probabilities which agree with çaç2
and
çbç2.]

Quantum theorists (see, e.g., Maximilian Schlosshauer, Kristian Camilleri,
http://arxiv.org/PS_cache/arxiv/pdf/0804/0804.1609v1.pdf) have realized that Eq. 1 is not a realistic description of the situation
because it omits entanglements between the two terms on the right and terms
describing the environment, including air molecules, physical apparatus,
photons, and the rest of the universe. When such interactions are included, the
system decoheres and interference between the two terms disappears. Without
interference, the terms describing the macroscopic objects (the detector and me)
become similar to a classical representation of macroscopic objects except that the
terms still refer to wavefunctions instead of positions, velocities, and
orientations. Also, because there has been no collapse, all of the terms remain
present and all of them contain interactions with the rest of
the universe. Thus, each term represents an entire universe that is very subtly
different from the universe represented by the other term. In this sense, the
theory is indeed a many-worlds theory.

It is easy to see that the number of branches rapidly proliferates as the
observations continue. In addition, most observations on most types of systems
will result in not just two branches, but many more, as many as are allowed by
Schrödinger’s equation. In fact, the number of branches at each observation is usually infinite.
Also, like the Copenhagen theory,
many-worlds theory is nonlocal because all parts of an entire branch (world) are
materialized simultaneously.

While the many-worlds interpretation is very economical in
terms of the number of concepts required in the theory, it is grossly
extravagant in terms of the complexity of the world it describes. Furthermore,
the existence of the other branches is intrinsically unverifiable--they are
hypothesized merely to preserve the mathematics of quantum theory. It is these features
that most physicists find hard to accept.

Question: Is there any way the many-worlds interpretation could be
true?

In the many-worlds interpretation, after a branching, I am in only my branch, and I observe only
my branch. As far as I am concerned, the other
branches are not materialized. The advantage of many-worlds is that the
unobserved branches can still be represented by wavefunctions even though they are
not observed. Thus, many-worlds theory does not require any mysterious reduction
mechanism to get rid of the unobserved wavefunctions, even though some
mysterious mechanism is required to materialize my branch. Cosmologists think
this mysterious mechanism could be epiphenomenal consciousness that arose after
the wavefunction evolved into enough complexity (this assumes that space-time is
objectively real). If we stipulate that the
unobserved branches remain unmaterialized, the many-worlds and Copenhagen
interpretations are very similar, and for our purposes can be considered to be
equivalent.

In Section 6.5, we saw that all quantum systems are nonlocal, not just those
of
the Aspect and
Gröblacher
experiments described in
Section 4.3.
The Copenhagen interpretation includes observations but contains no physical
mechanism for nonlocal wavefunction collapse. Hidden variables theory is
intrinsically nonlocal because of the nonlocal quantum force, but includes no
observations. Many-worlds theory includes observations but its explanation for
nonlocality is that the wavefunction, which is a purely mathematical, not a
physical object, is nonlocal.
Thus, physics
has no physical explanation for the nonlocality of observation. (This is reminiscent of Gödel’s theorem, which
we discussed in Section
5.6.) We must now begin to question our
assumptions about the reality of space and time. We shall say more about this in
Section 7.1 and Chapter 12.

As we have seen in Sections
6.4
and
6.5, if it is consciousness that
collapses the wavefunction (or that materializes a branch as in
Section 6.7), then consciousness
must be nonphysical. If it is nonlocal universal consciousness, we are faced with some other far-reaching
conclusions. What two individual observers see is determined by
universal consciousness, not by any kind of individual consciousness that might
exist. This applies to all of our sensory perceptions without exception. Since
everything we perceive is determined by universal consciousness, it makes no
sense to say that there is a material world independent of consciousness. Thus
the dualism of mind and matter is excluded.

It is only a small step now to suppose that, if all of our sensory
perceptions are determined by universal consciousness, then so also are all of our thoughts
and feelings because there is no intrinsic difference between them (as
we shall see in Chapters 9 and 23). If all experiences are determined by
universal consciousness, then we must conclude that nothing in our lives that we
consider to be "ours" as individuals is truly ours. If everything
flows from universal consciousness, "our" lives are not our lives at
all but are lives of universal consciousness. "My" consciousness
cannot really be mine, nor can there be any free will if none of "my"
thoughts is mine. Even the thought that I exist is not mine. With these
astounding conclusions, we are forced to ask the questions, "Do I really
exist?", and, "What am I, really?" We shall consider these
questions later in the course.

Question: If you really knew that you are universal,
nonlocal consciousness,
could you still
suffer?

Christopher Fuchs (http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.5209v1.pdf)
is pioneering an interpretation which contains no wavefunction at all. Quantum
probabilities are interpreted as Bayesian probabilities, which are measures of
states of belief, as contrasted with the more common case of quantum
probabiliies as measures of the physical properties of
a system. Bayesian probabilities are calculated as updates from prior
probabilities using a standard set of procedures and formulas (http://en.wikipedia.org/wiki/Bayesian_probability).
Fuchs has given these formulas a quantum interpretation.

Without wavefunctions, quantum mechanics has no problems or paradoxes of
nonlocaliy, collapse, or branching. This, perhaps, is the strongest argument for
a subjective interpretation.

[Historical note: British mathematician and Presbyterian minister Thomas
Bayes (1702-1761) proved the special case, which is called Bayes' theorem, of
the more general "principle of insufficient reason" of French mathematician and
astronomer Pierre-Simon Laplace (1749-1827).]

In physics, objective reality is defined as that which
exists whether or not it is being observed. A fundamental problem with this
definition is that it can never be verified by observation because all of our
observations, without exception, are purely subjective and can never go beyond
the mind (see
Section 1.1).

Classical physics is assumed to describe objective reality
as it is (see
Section 2.2). There is broad agreement among physicists on what classical
objective reality is. However, quantum theory is purely mathematical and
requires an interpretation to relate it to some form of reality (see
Section 6.1.). Most
interpretations relate the theory to some kind of objective reality, even if the
reality consists only of objectively real brain states. Since there are many
interpretations and hence many objective realities, how are we to know which one
is correct?

As we saw in Section 4.1,
interference suggests that physical waves are
interfering, whether or not they are identified with the wavefunction. Identifying them with the wavefunction is tempting because they
produce the same kind of interference pattern that the wavefunction would
produce were it a physical object. Yet, this leads to the nonphysicality of nonlocality,
collapse, or branching. Perhaps this dilemma is Nature’s way of
hinting to us that there is no such thing as external, physical reality.

In Section 6.1.3, we mentioned the possibility that the wavefunction
is not a physical wave but is merely a tool for calculating the probabilities for
certain specified events to be observed. If this is so, there is no external quantum wave
either before or after an observation. In this interpretation, only many
measurements on identical systems can be compared with the theory because the
theory says nothing about a single measurement. Therefore, this is sometimes
called the statistical interpretation.

A few physicists hold this viewpoint because it avoids all of the problems of
nonlocality, collapse, and branching ("Quantum Theory Needs No 'Interpretation'
by Christopher Fuchs and Asher Peres, Physics Today, March 2000, p. 70, and
"Letters", Physics Today, September 2000, p. 11). Another
viewpoint, espoused by David Mermin, "What's Bad About This Habit",
Physics Today, May 2009, p 8, states that all of our theories represent only our
state of knowledge, but they need not describe reality as it is. These physicists do not deny the possibility
of the existence of an external reality independent of what observers perceive,
but they do not state what its significance would be.

Fundamental to the assumption of an objective reality is
the assumption that spacetime exists. In quantum theory, spacetime is the
absolute, unchanging context in which everything happens. In general relativity (gravity theory, see
Section 2.6), space, time, matter,
and energy all depend on each other and are the content of the theory. The two theories are incompatible
because absolute context is not relative content. Hence, a unified theory of quantum gravity has
not been found and probably will not be found unless context and content can
somehow be
reconciled. One way to resolve this incompatibility is to see that spacetime is purely subjective rather than objective (see
Section 12.1).
If spacetime is a concept in the mind rather than the context of the mind, then
objective reality is also a concept because separation between objects must
occur in spacetime. This viewpoint is consistent with the teaching of nonduality,
in which separation is conceptual, not real (see
Chapter 9).

A subjective interpretation of quantum theory would
relate the theory to mind states (not brain states) and would thereby avoid the problems of
objective reality. It would be related to the philosophy of idealism,
the philosophy that all is consciousness and there is nothing but consciousness (see
Section 1.4), but not equivalent to it because the subjective interpretation need not say anything
about pure consciousness. A subjective interpretation would be an epistemological
interpretation, i.e., an interpretation in terms of subjective knowledge,
whereas all other interpretations are ontological, i.e., they are theories of
objective existence. The interpretation of Christopher Fuchs,
et al. (see
Section 6.10) is only partly subjective because it
assumes that there is an objective quantum system although everything we can
know about it is subjective. The only working physicist I know who states that
the universe is purely mental is Richard Conn Henry (http://www.newdualism.org/papers/R.Henry/436029a.html).

Even if there is no objective reality there might be other minds. As with objective reality, we cannot objectively verify that other minds exist because the contents
of them (thoughts, feelings, emotions, body sensations, perceptions) are not
directly perceivable to us. We can only infer or intuit that they might exist.

We normally assume that there are at least two minds, mine and yours.
So, how do our minds communicate? In the absence of objective reality, there can
be no physical mechanism for communication, so we can say that if minds can
communicate with each other, they cannot be truly separate from each other.
Furthermore, communication requires a language--but the language we use is that
of objective reality. So, even in the subjective interpretation, we use objective language! This requires agreement on the definitions of the "objects"
observed, a comparison of observations, and agreement on the results of
observations (see
Section 1.1).

We cannot prove the existence of an external objective reality because all of
our experiences are purely subjective and can be explained in purely subjective
terms without invoking the concept of an objective reality. Assuming there is no external reality, our concepts of nature are limited by the kinds of experiments we do and by
the type of theory that we use to interpret them. Our present picture of the
microscopic world as consisting of atoms, molecules, and elementary particles is
determined in an essential way by these limits. Radically different kinds of
experiments and theories might produce a radically different kind of picture.

The three general classes of interpretations of quantum theory are
the following:
1) Purely objective. In classical physics, this would be a purely
materialistic interpretation. In quantum physics, it could be a hidden
variables interpretation, or a many worlds interpretation when there are
no observers, as in the early universe. If consciousness exists, it is
an epiphenomenon of the material world and has no agency. The material
world determines all of our experiences.
2) Partly objective and partly subjective. Classically, this would be a
Cartesian dualistic, or mind/body interpretation. In quantum physics, it
could be a Copenhagen interpretation if consciousness collapses the
wavefunction, or a many worlds interpretation if consciousness causes a
branching. In both cases, it is consciousness that manifests the
material world.
3) Purely subjective. Classically, this would be an idealistic
interpretation, such as Plato's or Berkeley's. In quantum physics, a
purely subjective interpretation need have no wavefunction, but if it
did, the wavefunction would be purely a tool for calculating the
probability that a subjective experience would occur.

How would your life be different if each of the three different
interpretations were true?

As we discussed in Section
1.1, because all of our experience is subjective, it is clear that the existence of an external reality can never be
verified by observation and
thus it can only be a metaphysical
assumption. Furthermore, if objective reality cannot be observed, it cannot affect any observation because an effect on an observation
is an observation. Thus, the concept of an
external reality is both unsupportable and unwarranted. However, even though an
external reality can itself have no effects, the concept of one certainly can. In
fact, in Chapter 9 we shall see that it is this
concept that causes all of the suffering there is.

It is ironic to think that the careful, painstaking, empirical and
theoretical study of external physical reality, which is what we call physics,
could lead to the conclusion that there is no such reality! It appears
that the hypothesis of external reality contains the seeds of its own
destruction! What physicists really do is to study their own minds because
that is the only place where objects are present. Perhaps the domain of
physics will some day shift from objectivity to subjectivity, and physicists
will begin to welcome the sages as friends rather than viewing them with suspicion.

Questions: Assuming there is no consciousness but
nonlocal universal consciousness, what might be the definition of mind?
If we infer that there are such things as different minds, what is the basis for this
inference? Why does it seem so compelling? Would the inference of an
objective reality be just as compelling? If so, why? If not, why not?

Exercise: Become
aware of your sense of awareness. Is it a thought or feeling, or
neither? Can it be present without thoughts or feelings? Can thoughts or
feelings be present without it? Look inward and use your intuition!

This page last updated October 16, 2010.
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